The present invention relates to a method and apparatus for selectively separating targeted species of aquatic life from non-targeted species during underwater harvesting operations. Specifically, the invention separates targeted mature shrimp from other non-targeted aquatic organisms in shrimp trawls allowing the non-targeted organism to pass out the open back end of the trawl while capturing the targeted mature shrimp in a separated closed portion of the trawl.
Traditionally shrimp nets or trawls have had an open front end which is opened during towing operations to allow aquatic organisms to be captured within the confines of the trawl or net. The cod end or back end of the trawl is closable and is closed during the towing of the net underwater. Thus, all species are accumulated in the net and must be separated when the net is removed from the water. Normally, the net is withdrawn from the water and the closable end (cod end) is opened to release the harvested aquatic life. Non-targeted species such as fish, turtles, porpoises and jellyfish are returned to the water while the mature shrimp are retained.
Unfortunately, many of the non-targeted species die before they may be returned to the water. In many cases, the non-targeted species are crushed within the trawl by incoming aquatic life and even non-living debris from the floor of the water body. It is not uncommon for thousands of juvenile fish (approximately 1" long) to be found dead at the back of the net when the shrimp net is pulled up. This results in a reduced fish population and lowering certain fish catch limits. Ultimately, all of this has a long-term negative financial impact on the fishing industry. Also, a percentage of the targeted shrimp species are also crushed, reducing the efficiency of the harvest. To reduce these problems, shrimpers have tended to shorten the time period of a particular tow and withdraw the trawls more often to separate the targeted and non-targeted species and debris. There are considerable costs associated with the time lost in pulling in and putting out the nets more often.
Further environmental problems have resulted in that certain non-targeted species such as the turtle are endangered as a result of being captured and dying in increased shrimp harvesting processes. In an effort to protect certain species of turtle, regulations have been put into effect which require the use of a turtle exclusion device (TED) on shrimp trawls. Essentially a TED is a mechanism placed on the top side of the shrimp trawl which functions as an open door to allow turtles captured through the open, front end of the net to pass out an opening in the body of the net while other species including fish, shrimp, horseshoe crabs, jellyfish, etc., pass to the closed cod end of the net. While TED's have reduced the number of turtles which are captured and die during shrimp harvesting operations, shrimp just as easily pass through the open TED; thereby reducing the productivity of the shrimping operation.
The present invention utilizes a method and apparatus which selectively directs mature shrimp into a collection net portion of the trawl while allowing the non-targeted species and debris to pass out the back end of the trawl.
The present invention not only allows non-targeted species to pass through the trawl, but also allows immature shrimp to avoid capture and harvesting. Such a selection process ultimately results in an increase in available mature shrimp for subsequent harvesting. Thus the numerous problems associated with the current trawls are eliminated while increasing the productivity of the harvesting operations.